open-source telephony API platform / CPaaS

FreeSWITCH is an open-source software telephony switch that routes and processes voice, video, and messaging calls over IP networks using standard protocols such as SIP and RTP. It serves as both a call routing and switching engine and a programmable telephony API, enabling developers to build custom telephony applications with event-driven call control and media manipulation. As a SIP media server, it handles media streaming, transcoding, and conferencing, and functions as a unified communications platform integrating voice, video, messaging, and conferencing into a single switchable infrastr

Fonoster is a conversational AI framework and multi-tenant communications platform as a service. It serves as a programmable voice gateway and SIP telephony platform, enabling the creation of voice-based assistants and automated communication workflows using large language models. The project distinguishes itself through a vendor-agnostic speech integration engine that abstracts speech-to-text and text-to-speech providers. It features a multi-tenant architecture that isolates telephony resources and user identities into distinct organizational workspaces. The system covers a broad range of t